Interference between competing motor memories developed through learning with different limbs

Abstract:

Learning from motor errors that occur across different limbs is essential for effective tool use, sports training and rehabilitation. To probe the neural organization of error-driven learning across limbs, we asked whether learning opposing visuomotor mappings with the two arms would interfere. Young right-handers first adapted to opposite visuomotor rotations A and B with different arms, and were then re-exposed to A 24 hours later. We observed that re-learning of A was never faster, nor were initial errors smaller than prior A learning, which would be expected if there was no interference from B. Rather, errors were greater than or similar to, and learning rate was slower than or comparable to previous A learning depending on the order in which the arms learned. This indicated robust interference between the motor memories of A and B when they were learned with different arms in close succession. We then proceeded to uncover that the order-dependent asymmetry in performance upon re-exposure resulted from asymmetric transfer of learning from the left arm to the right but not vice-versa, and that the observed interference was retrograde in nature. Such retrograde interference likely occurs because the two arms require the same neural resources for learning, a suggestion consistent with that of our past work showing impaired learning following left inferior parietal damage regardless of the arm used. These results thus point to a common neural basis for formation of new motor memories with different limbs, and hold significant implications for how newly formed motor memories interact.